Unique telescope to open the X(-ray) Files

Unique telescope to open the X(-ray) Files

Artist's concept of AXAF in orbit., The nested mirrors are at center
behind the dotted circles.

The finest set of mirrors ever built for X-ray astronomy
has arrived at NASA's Marshall Space Flight Center for several weeks of
calibration before being assembled into a telescope for launch in late 1998.

The High-Resolution Mirror Assembly (HRMA), as it is known, will be the
heart of the Advanced X-ray Astrophysics Facility (AXAF) which is managed
by Marshall Space Flight Center. HRMA was built by Eastman Kodak and Hughes
Danbury Optical Systems. In 1997-98, they will be assembled by TRW Defense
and Space Systems into the AXAF spacecraft. AXAF is designed to give astronomers
as clear a view of the universe in X-rays as they now have in visible light
through the Hubble Space Telescope.

Indeed, one of the Hubble's recent discoveries may move near the top of
the list of things to do for AXAF. Hubble recently discovered that some
quasars reside within quite ordinary galaxies. Quasars (quasi-stellar objects)
are unusually energetic objects which emit up to 1,000 times as much energy
as an entire galaxy, but from a volume about the size of our solar system.

More clues to what is happening inside quasars may lie in the X-rays emitted
by the most violent forces in the universe.

Before AXAF can embark on that mission, though, its mirrors must be measured
with great precision so astronomers will know the exact shape and quality
of the mirrors. Then, once the telescope is in space, they will be able
to tell when they discover unusual objects, and be able to measure exactly
how unusual.

These measurements will be done in Marshall's X-ray Calibration Facility,
the world's largest, over the next few weeks.

AXAF will use four sets of mirrors, each set nested inside the other, to
focus X-rays by grazing incidence reflection, the same principle that makes
sunlight glare off clear windshields. AXAF's smallest mirror - 63 cm (24.8
in.) in diameter - is larger than the biggest - 58 cm (22.8 in.) flown on
the Einstein observatory (HEAO-2) in 1978-81.

Mapping the details of the mirror will start with an X-ray source pretty
much like what a dentist uses to check your teeth. But that's next week's
story.